This is a proposal to purchase the hardware and software that will constitute a new x-ray tomographic microscope (XTM). The existing XTM allows researchers to three-dimensionally image biological tissues with micrometer resolution. This instrument is a major tool now being utilized in several NIH funded research grants. With the XTM, researchers are visualizing, in vivo, the earliest changes in trabecular bone architecture following estrogen deficiency in the ovariectomized rat model of osteoporosis. In other projects, researchers are using the XTM to quantify mineral density distribution in normal, diseased, and demineralized dentin to develop better clinical approaches in restorative dentistry. Also, the XTM is being used in genetic studies of peak bone mass, studies of the mechanisms of coronary balloon angioplasty, studies of combined effects of electromagnetic fields and parathyroid hormone on bone remodeling, and biomechanical studies of trabecular bone. The proposed instrumentation will enhance the quality of the XTM images by improving the instrument optics and staging, and by improving the accuracy and speed of the reconstruction process. The new instrumentation will also increase the variety of studies that can be performed by increasing the load bearing capacity and travel of the stages. Moreover, there is an anticipated factor of ten improvement in system efficiency, which will allow many more specimens to be imaged, and reduce costs to individual projects. In addition, the new data management system will allow sharing of data among investigators at remote locations.